An automotive vehicle engine transfers a portion of the engine output to a plurality of belt driven accessories utilizing an endless serpentine belt. Typically, each component includes an input drive shaft and a pulley coupled to a distal end of the drive shaft for driving engagement with the belt. An example of such a belt driven accessory is an alternator.
A decoupler is operatively coupled between the pulley and the alternator to allow the alternator drive shaft to “overrun” or rotate at a faster speed than the pulley and to allow the speed of the pulley to oscillate with respect to the alternator drive shaft due to oscillations in the engine speed. Examples of decouplers are disclosed in U.S. Pat. No. 6,083,130, issued to Mevissen et al. on Jul. 4, 2000, U.S. Pat. No. 5,139,463, issued to Bytzek et al. on Aug. 18, 1992 and International Patent application no. WO 2004/011818.
In PCT application no. WO 2004/011818, the decoupler reduces torsional fluctuations in the endless drive system. However, in certain applications in which the engine has an aggressive start profile or during conditions of rapid acceleration during a wide open throttle shift, the torques transmitted will over-stress the torsion spring reducing long term durability of the decoupler.